1. Field of the Invention
The present invention relates to backup units and ink-jet printers, and more particularly to a backup unit equipped with a pump mechanism and/or a nozzle cap mechanism and to an ink-jet printer having a such a backup unit.
2. Description of the Prior Art
An ink-jet printer is constructed such that characters or the like are printed on recording medium such as paper by injecting an ink from a thin nozzle of a print head. There are several kinds of inconveniences that could occur in the ink-jet printer. For example, the ink becomes dried and thickened in the nozzle. Or paper powder may be attached to the nozzle that is wet from the ink, resulting in the nozzle being covered by the powder. Or air bubbles may enter the print head through the nozzle as a result of disturbance like an oscillation. If nothing is done to overcome these inconveniences, the nozzle may be wholly or partly clogged, causing the ink to be injected improperly. Or the pressure for injecting the ink may be canceled by the air bubbles, causing the ink to be injected imperfectly. Either way, the printing quality is degraded significantly. Accordingly, a backup unit is required to inject the ink powder from the nozzle in a stable manner.
A backup unit removes the thickened ink, the air bubbles, the paper powder or the like from the print head, by forcefully sucking the ink from the nozzle. The backup unit is a kind of print head protection mechanism for performing a restoring action in which a normal condition of the nozzle is restored by removing the clogging of the nozzle. This restoring action will be referred to as a purging action. The purging action is performed during an initialization immediately after the turning ON of the ink-jet printer or performed at a timing specified by a user.
A conventional backup unit comprises a pump for the purging action and valves provided at an inlet and an outlet of the pump. There is a problem in that, because of the valves provided, the backup unit becomes relatively large, requiring a relatively large space inside the ink-jet printer. Another problem is that, since these valves are constructed to open and close in response to the pressure produced in the pump, the response thereof is poor. Therefore, it takes a relatively long time for the valves to be activated. Further, it is to be noted that the higher the speed of the flow of the ink during the purging action, the higher the effect of storing the nozzle to normal. A problem is that, if the conventional pump structure is employed to realize a high flow speed, the size of the pump itself becomes large because the pump has to produce a large negative pressure. If the pump is large, it is required that the power for driving the pump be large.
The backup unit includes a nozzle cap for sealing the nozzle in order to prevent the ink from being dried or thickened in the nozzle when the print head is not in use; for example, when the ink-jet printer is turned OFF. The nozzle cap is connected to a pump for carrying out the purging action in a tube. A failure for the nozzle cap to seal the nozzle properly by being attached thereto in a most suitable position may occur due to errors in mounting a movable carriage to which the print head is fitted, the print head or the nozzle cap itself. The failure may also occur due to a bending force of the tube connected to the nozzle cap. In other words, there is a problem in that the sealing of the nozzle by the nozzle cap may be imperfect due to the mounting errors or the like. If the sealing of the nozzle is imperfect, the ink may be dried or thickened in the nozzle, or the negative pressure required for the purging action by the pump is insufficient. Thus, the backup unit may not be operated properly.